Preparation of hexafluorobutadiene from symmetrical dichlorodifluoroethylene



"&"Co'. "lt is therefore an object of this'inventiori to provide faneconomical and convenient method forthe' preparationof h'exafiuoio-"lj3butadienei' A related'objectis -to p'rcivitle a new process wherebyhexafluoro-l;3-butadine process involving the" steps of:

United States PatentO PREPARATION' OF HEXAFLUfiROBUTADIE'NE FROMSYMNIETRICAL DICHLORODIFLUORO ETHYLENE linear". manna-1 A. Davis, andKeith A. A Jlswede,

Midland, Mich., assignors td-The Dow Chemical Coinpan'y; Midland, Mich,a' corporation of Delaware No Drawing. Application June 24, 1953,SerialNo'. 363,910

invention relates to an improved processfor the preparation ofhexafiuorobutadiene'.

tical methods have been developed for the synthesis ofheiiafluoro-l,3-butadiene'. Of. the two methods reported in theliterature, oneinvolve s'the thermal dimerization ofchlorotrifluoroethylene at temperatures in excess of 500 C. while theother. method involves the fluorine-catalyzed dimcrization ofsymmetrical dichlorodifiuoroethylene at mperatures of from 55" C. toabout 80 C.

.Neithefm'thodgives an o'ver'all'yiel-d' higher tliali'aboilt 30percent; It is therefore ap arent tlrata better method must bediscovered for th'e' pi'eparationof'heiiafluoro lfibutadiene if thiscompound is'to become commercially important. In fact, if a moreconvenient method can be developed forits synthesis, hexafiuorol,3buta'dieiie may H" eemtneaar, Elorine and. Itscempounds, Methiien page108* (1951)).- a

came-prepared in good conversions and yields from sym-,int'iicaldichlorodifiuoroethylene; Other objects 'and advantages areapparent from the following description wntcnniustrates' ann disclosesbut does'n'o'tlin'iit" the nve tion:

According to the present invention, hexafluoro-lfi butadiene" may be'produced in good conversions and yields at, rnoderate'temp'erature's andpressures'by a new Thermally dimeriiing' l,2 -dicliloro-l,2difluoroethylene; to 'l,3,4,4-tetrachloro 1,2,3,4 tetrafluorobutene l.

(2) chlorinating 1,3,4,4'- tetrachloro-l,2,3,4-totraflliorobutene l to1;1,2,3,4;4;hexach1ore 1,2,3,4 tetraniiorebutane. A v i (3)Fluorinating" l,l,2,3,4,4 hexachloro-l,2,3,4;tetra- (.4) Anddechlorinating I the 1}2,3,4-tetrachloro- 1}1,2,- 3,4',4-he'itafidorobutane" to hexafiuoro-lfifbutadienel These steps areillustrated by the followings im'plified Clie'fn'ical diagram:

2,777,004 Patented Jan. s, 1957 ice (1) Dimcrization with heat andpressure (2) Chlorination with gaseous chlorine Fluorination e. g. (3) Ii with sbrs'on OFaCh-OF o1-o FOlG F201 (4) Dechlorination with zinc andalcohol Thedimerization step (1) may be carried out by heating'. CFCl=CFCl ina closed vessel under its autogenous pressure at a temperature inthe range of about 200 C. to about 400 C. for a time sufficiently longto bring about the desired degree of reaction as expressed by thefollowing theoretical equation:

heat; C F 01:0 F-C F Ol -C F0]: pressure 't A lr'nost any steel reactionvessel'str'ong. enough to cont'a'in'the symmetricaldichlorodifiuoroethylene at the temperature"of'the reaction issatisfactory as a reactor. Agitation is generally applied to thecontents of the reaction 30"vessel to maintain a uniform temperaturethroughout.

Maximum conversion to the dimer CFCl=CF-'CFC1CFC12 usually be obtainedat a temperature between about 250 C. and 300 C. The optimum temperatureof the reaction varies inversely with the length of' the heating period;c. -g.', for comparablyhighconversions, a longer reaction time isrequired at 250 C. than at 300 C. Heating periods of from 5 to 20 hoursormore may be employed, although lofigreactiontirnes produceconsiderabl'eamounts of high boiling material which lowers the overallyield of the desired product CFCl=CF-CFClCFCl2 For both maximumconversions and yields, therefore, the

symmetrical dichlorodifluoroethylene is usually heated at a temperatureof about 275 C. while the pressure rises to amaxim'u'mvalue, e. g.approximately'lSOO pounds per square inch gauge at 275 C., and thenfalls off to about'400' p. s. i. g. If the reaction product is rapidlycooled at the end of this heating period, usually no longer than aboutten hours, the percentage of higher v boiling 'material canbe kept to aminimum, e. g; less than 10 weight percent. Under optimum conditions,the conver sion and yield values for CFCl=CFCFClCFCl2 correspond to 77percent and 87 percent respectively. As

herein'af't'erused, these terms have the following meaning:

moles of product recovered Conversion: moles of reactant charged X0100moles'of product recovered moles of reactant consumed X7100 In thedimerization of CFCl=CFCl, the number of moles V of product CFC1=CFCFCl-CFC12 have, of course, to be-multipliedlby two in calculatingconversion and yield values.

Following dimerization, the product is subjected to the chlorinationstep (2) of the process. This step is accomplished in the presence ofactinic light, such as ultraviolet light or direct sunlight, by bubblinggaseous chlorine into liquid CFC1=CFCFCl-CFC12 until approximatelyequimolecular proportions have reacted, i. e. until chlorine is nolonger absorbed. The reaction proceeds substantially to completionaccording to the following equation:

A glass flask or ceramic-lined vessel preferably equipped with awater-cooled reflux condenser may be employed as a reactor. Thetemperature at which this exothermic chlorination reaction may becarried out is not critical and temperatures between 20 C. and 100 C.are both convenient and practical. Although somewhat lower temperaturesor even a temperature as high as the reflux temperature of the reactionmixture may be employed,

no advantage appears to be derived by operating at such I conditions.

The chlorinated product may be purified or employed per se in thefluorination step (3 This step is generally conducted in the liquidphase in a closed reaction vessel under the autogenous pressure of thereaction mixture employing a fluorinating agent such'as antimonyfluorohalide or antimony fluoride and chlorine. The fluorination may beaccomplished in the vapor phase, as by means of HF and a catalyst suchas chromium fluoride. However, liquid phase fluorination with a fluorideof anti mony is usually preferred for best conversions and yields of thedesired product. The antimony fluoride should preferably contain atleast 5 percent by weight of pentavalent antimony and is desirablySbFsClz. In general, theoretical or slightly greater than theoreticalproportions of fluorine and temperatures in the range of 150 to 350 C.are satisfactory when a fluoride of antimony is employed as thefluorinating agent. When approximately equimolecular proportions of.CFCl2-CFClCFClCFCl2 and SbFsClz are reacted to completion at 250 C.under conditions of good agitation, greater than 90 weight percent ofthe chlorofluorobutane reactant is fluorinated to CF2Cl--CFC1CFCl-CF2C1according to the reaction:

Following fluorination, the product CF2Cl-CFClCFCl-CF2C1 greater than 2atomic proportions of zinc per molecular proportion ofCFnClCFCl--CFC1CF2C1. The dc chlorination reaction is highly exothermicand may be represented by the following equation:

ethanol 0 FaCl-C F 01-0 F Ol-C F201 2Zn This step may be carried out ina glass flask or ceramiclined vessel equipped'with a water-cooled refluxcon-' denser.

The dechlorination proceeds quite rapidly at a temperature in the rangeof 20 to 100 C. and isconveniently conducted at the reflux temperatureof the reac:

This step may be accomplished with zinc .to react with essentially allof the chlorine atoms of the chlorofluoro-butane is generally employed,e. g. slightly 4 tion mixture, i. e. approximately C. when ethanol isthe alcoholic solvent. The rate at which hexafluoro-l,3-butadiene isformed and liberated from the reaction vessel is roughly proportional tothe rate of addition of the chlorofluorobutane reactant, i. e.dechlorination occurs almost instantaneously upon combining thereactants. Following addition of all the chlorofluorobutane, thereaction mixture is ordinarily heated for a short period of time toinsure essentially complete reaction. The producthexafluoro-1,3-butadiene boils at about 6 C. and may be collected bycondensation in a refrigerated receiver. The product so collected may bepurified if desired by fractional distillation.

The various step-wise reactions of the instant process may be carriedout in a consecutive manner without separating the desired reactionproduct of each step from t the total organic product mixture prior toany subsequent reaction. For example, the total product from thedimerization step may be subjected to chlorination, the entire productfrom the chlorination step may be fluorinated, and the total organicproduct from the fluorination step may be dechlorinated withoutseparating the organic reaction products of any step from start untilfinish. For best results, however, the desired product from each step ofthe process is preferably separated from the unconverted reactant andany other reaction products before being further reacted. In thismanner, as will be observed from the example, high overall conversionsand yields of the desired end-product, hexafluoro-1,3-butadiene, may beobtained.

The following example illustrates the process of the invention, but isnot to be construed as limitative.

EXAMPLE Hexafluoro-1,3-butadiene was produced from symmetricaldichlorodifluoroethylene according to the method hereinafter described:

Dimerz'zation of 1,Z-dichloro-I,Z-difluoroethylene A cylindrical 4-litersteel reaction vessel evacuated to 1 mm. mercury absolute pressure wascooled to below 10 C. and charged with 1645 grams (12.36 moles) ofliquid 1,Z-dichloro-l,Z-difluoroethylene. The

heating period of about 6 hours duration. During this time, the pressurein the sealed reactor rose to a maximum of 1920 pounds per square inchgauge. When the pressure fell off to about 400 p. s. i. g., heating wasdiscontinued. The reaction was then quenched by rapidly cooling thereaction vessel and its contents below C. Upon further cooling, e. g. toa temperature well below 20 C., the liquid reaction product weighing1625 grams was removed and subjected to fractional distillation. Inaddition to 217 grams of the starting material CHF1=CFC1, there wereobtained 1247 grams (4.69 moles) of dimeric CFCl=CF--CFC1-CFC1:, 25grams of an intermediate fraction boiling between the symmetricaldichlorodifluoroethylene and the dimer, and 136 grams of higher boilingmaterial.

Based on the moles of CFC1=CFC1 charged, this represents a conversion toCFCl=CFCFClCFCl2 of 75.9 mole percent and a total recovery of 98.8weight percent. The

sesame Chlorination of 1,3,4,4:zetmchzam-i,as,4aqrqfl@r butane-1 Into a2-liter glass flask equipped with a reflux condenser was charged 1488grams (5.6 moles) of CFCl=CF--CRC1CFC12 prepared from a number of runsas described above. Gaseous chlorine was rapidly bubbled into the liquidtetrachlorotetrafluorobutene-1 under exposure to direct sunlight. At theend of about 3 hours, approximately the theoretical quantity of chlorinehad reacted. Upon fractional distillation of the reaction product therewas obtained 51 grams (0.19 mole) of unreacted CFCl=CFCFClCFCl2 and 1813grams (5.38 moles) of CFCl2-CFClCFCl-CFC12 boiling at 204 C. at 745 mm.mercury absolute. Based on the moles of CFCl=CFCFClCFCl2 charged, thisrepresents a conversion to CFClz-CFClCFCl-CFC12 of 96.1 mole percent anda total recovery of 99.5 rnole percent. The yield of CFCl2CFClCFCl-CFC12based on the CFCl==CF-CFCl-CF C12 consumed is 99.4 mole percent.

Fluorination of 1,],2,3,4,4-tetrachl0ro-1,2,3,4-tetrafluorobutaneApproximately 22927 grams (68.0 moles) of CFCl2--CFCl-CFCl--CFC12prepared in several runs according to the above procedure and 17050grams (68.2 moles) of SbFsClz were charged into a 5 gallon steelreaction vessel. The reaction mixture so charged was heated to 250 C.and maintained at this temperature under conditions of good agitationfor the duration of the heating period. At the end of about 5 hours, theorganic reaction product was cooled, .washed with water to removeantimony salts, and dried with anhydrous calcium sulfate. Thereupon, thedry product weighing 19,568 grams was fractionally distilled and thefollowing fractions were obtained:

Boiling range 739-740 mm. Hg abs. Empirical Grams Mole Formula percent040113 76 0. 3 C4ClzFa 0. 4 C4Cl3F1 0. 1 C4Cl4Fs 86. 6 168 C4ClsF5. 3. 4Intermediate fractions 664 The C4Cl4F6 fraction boiling at 133 c. at 740mm.

mercury absolute was identified as CFzClCFCl-CFCl-CF2C1 consumed, theyield of CF2ClCFCl-CFClCF2Cl was 89.6 mole percent.

The C4CI5F5 fraction boiling at 168 C. at 739 mm. mercury absolute wasfound to be By dechlorination of this compound with zinc and alcohol,there was obtained a diolefinic C4C1Fe compound 6 boilingat. 35: 1-38)G. at ,45. man mercury. absolute which Wassubsequ nfly identified asDechlorinqtionof 1 ,2,3,4-tetrachloro-1,1,2,3,4,4-

' hexafluorobutane Into a;5 i-lit er glass flask equipped with adropping funnel, reflux condenser, and mechanical stirring device andcontaining 1430 grams (22 moles) of powdered zinc, was gradually added2606 grams (8.56 moles) of the CFzCl-CFCl--CFCICF2C1 prepared as abovedissolved in 4100 ml. of absolute ethanol. Addition required a period of6 hours, the rate of addition being such as to maintain a steady refluxof the absolute ethanol.

During this time, gaseous CF2=CF--CH=CFz was continually given oil bythe reaction mixture. This normally gaseous compound passed out of thereaction flask through a water-cooled reflux condenser and into arefrigerated trap where it was collected as a liquid. When all of thealcoholic solution of had been added to the flask, the reaction mixturewas heated under reflux for a short period of time. tional distillationof the product liquid in the cold trap gave 1251 grams (7.72 moles) ofCF2 CFCF=CF2 (structure confirmed by vapor density determination andbromination to CFzBrCFBr-CFBrCF2Br). There was also obtained 70 grams(0.3 mole) of an unidentified dichlorohexafluorobutene having one of thefollowing structural formulas, viz. CFz=CFCFClCF2Cl or CF2ClCF=CFCF2Cl.Based on the moles of CFzClCFCl--CFCl-CF2C1 charged, the above datarepresent a conversion to CF2=CFCF=CF2 of 90.2 mole percent and a totalrecovery of 93.7 mole percent. The yield of CF2=CFCF=CFz based on theconsumed is 93.5 mole percent.

These results represent an overall yield for the production of the finalproduct CFz=CF--CF==CF2 from the initial CFCI=CFC1 reactant consumed ofgreater than 72 mole percent.

That which is claimed is:

1. A process for the preparation of hexafluoro-1,3- butadiene whichcomprises fluorinating 1,1,2,3,4,4-hexachloro-l,2,3,4-tetrafluorobutaneto 1,2,3,4-tetrachloro- 1,1,2,3,4,4-hexafluorobutane and dechlorinatingthis latter compound with zinc in the presence of alcohol to obtainhexafluoro-l,3-butadiene.

2. A process for the preparation of hexafluoro-l,3- butadiene whichcomprises chlorinating -1,3,4,4-tetrachloro-l,2,3,4-tetrafluorobutene-1to 1,1,2,3,4,4-hexachloro-l,2,3,4-tetrafluorobutane, fluorinating1,1,2,3,4,4- hexachloro 1,2,3,4 tetrafluorobutane to 1,2,3,4tetrachloro-l,1,2,3,4,4-hexafluorobutane, and dechlorinatingfluorobutane and dechlorinating this latter compound to Ihexafluoro-l,3-butadiene with zinc in the presence of a lower alkanolunder essentially anhydrous conditions.

4. In a process for preparing hexafluoro-l,3-butadiene whereby1,2-dichloro-1,2-difluoroethylene is converted to Frac- 7l,2,3,4-tetrach1oro-1,1,2,3,4,4-hexafluorobutane and this lattercompound is dechlorinated.to hexafluoro-LB-butadiene, the steps whichcomprise first heating 1,2-dichloro- 1,2-difluoroethylene in a closedvessel at a temperature in the range of from about 200 C. to t about 400C. for a time sufficiently long to form 1,3,4,4-tetrachloro-1,2,3,4-tetra.fiuorobutene-1, chlorinating the 1,3,4,4#tetrachloro1,2,3,4 tetrafluorobutene 1 to1,1,2,3,4,4-hexachloro-1,2,3,4-tetrafluorobutane, and fluorinating the1,1,2,3,4,4-hexachloro-l,2,3,4-tetrafluorobutene to 1,2,3,4

tetrachloro-l,1,2,3,4,4-hexafluorobutane.

and Organic Fuorine Compounds, Slesser and Schram, page 676 (1951).

1. A PROCESS FOR THE PREPARATION OF HEXAFLUORO-1,3BUTADIENE WHICHCOMPRISES FLUORINATING 1,1,2,3,4-HEXA-D CHLORO-1,2,3,4-TETRAFLUOROBUTANETO 1,2,3,4-TETRACHLORO1,1,2,3,4-HEXAFLUOROBUTANE AND DECHLORINATING THISLATTER COMPOUND WITH ZINC IN THE PRESENCE OF ALCOHOL TO OBTAINHEXAFLUORO-1,3-BUTADIENE.